An extended linear method to evaluate the viscoplastic behavior of boron steel at large strain with full-field measurements

The reliable parameter identification method of the constitutive behavior under large strain conditions is essential for accurate simulation in the hot stamping and warm-cutting process. In this paper, the linear stress-strain curve identification (LSSCI) method is extended to identify the viscoplastic behavior of boron steel at large strain based on the full-field measurements in the Gleeble system. An inverse LSSCI method to evaluate the strain rate sensitivity under different temperatures based on full-field measurements is presented. To overcome the fluctuation of the identified stress-strain curve at large strain, a constrained optimization method is proposed to solve the linear system. The numerical and experimental cases are performed to verify the accuracy and reliability of the proposed LSSCI method. The verification result shows that the identification error of the extended LSSCI method is generally less than 1%, and the maximum error is not more than 4%. The influence of strain rate, specimen shape, constitutive model, noise and discretization on the identification curves have been studied, the results show that the extended LSSCI method is robust when applied to viscoplastic material identification. To accurately describe the viscoplastic behavior of Boron steel at large strain, a unified viscoplastic (UVP) model is proposed based on the dislocation density evolution under elevated temperature. Finally, the tensile testing of shear and notched specimen are carried out to verify the accuracy and reliability of the proposed UVP model, the comparison of load-stroke curve shows that the large deformation behavior of the boron steel under various conditions can be accurately predicted by the UVP model with the parameters from the proposed LSSCI method. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This paper introduces an extended LSSCI method to accurately identify the viscoplastic behavior of boron steel under large strain conditions, and validates its accuracy and reliability through numerical and experimental cases. Additionally, a unified viscoplastic (UVP) model based on dislocation density evolution is proposed for describing the viscoplastic behavior of Boron steel at large strain.